Just make sure you're ignoring the fluff equally. Afterall, if the girls want to play a female space marine there should be no reason not to allow the males to play as male Adetus Fraterus.
The background denies one by saying the geneseed only works with male hormones and tissue types (ie, the Y chromosome) and denies the other by the law that the ecclesiarchy may not have 'men under arms'.
A genetic incompatabiltiy is a far greater obstacle than an imperial law, so I would say it would be far easier to have male sisters of battle than female marines.
But so long as things are being equalised. Anything less and it's not equality.
I have at any one time up to two women in my group and one of them specifically relishes the opportunity to play a Callidus assassin alongside a killteam. An imperial assassin may not be as strong and tough as a marine but they have better training and skills (yes, there are people that can beat space marines).
Hellebore
. Real world rarely has anything to do with how thing work in some place far far away in space/time.